1. Field of the Invention
This invention relates to a measuring instrument for measuring a length or a thickness of an object with the moving displacement amount of a spindle. More specifically, this invention relates to an attachment formation for a movable detection element in a formation for detecting the moving displacement amount of the spindle by a detecting means having a stationary detecting means and a movable detecting means.
2. Description of the Related Art
There is a known measuring instrument associated with a body; a spindle which is movably disposed in the body; and a detecting means, including a stationary detection element secured to the body and a movable detection element which is placed opposite the stationary detection element separated therefrom at a predetermined gap and synchronizes with the spindle and moves in the moving direction of the spindle, and being for detecting the relative moving displacement amount between both detecting elements as an electric signal.
The know type is, for example, a digital readout dial gauge to detect the moving displacement amount of a spindle, movably disposed in a body, as an electric signal by a detecting means, and display the detected value in a digital form, in which the detecting means is of an optical type, a capacitance type or the like and is provided with a scale having a stationary detection element (e.g., a light emitting and receiving portion, an electrode) disposed in the body and a movable detection element (e.g., a light emitting and receiving portion, an electrode) placed opposite the stationary detection element separated therefrom at a predetermined gap and synchronizing with the spindle and moving in the moving direction of the spindle.
Conventionally, in the measuring instrument as described above, on the grounds that when a gap between the stationary detection element and the movable detection element is changed, miscount occurs and the stable and precise measurement is not achieved, a formation capable of assembling while a processing dimension error of each component is being absorbed is employed.
More specifically, the stationary detection element is fixed in the body, and a metal scale holder is integrally fixed to the spindle or a metal scale holder is movably disposed in the body. The scale holder is forcibly pressed to abut to the end portion constantly by a spring or the like in order to be synchronized with the spindle and moved in the moving direction of the spindle. And then a scale having the movable detection element is adhered onto the nearly overall surface of the scale holder through an adhesive layer. Thereby, the measuring instrument is assembled to retain the constant gap between the stationary detection element and the movable detection element while the processing dimension error of each component is absorbed by the adhesive layer.
The conventional formation has advantages in that the contour precision is easily achieved and the rigidity is high due to the fact that the scale holder is made of metal, however, it also has disadvantages from the viewpoints of portability and operability in a measuring instrument used for measurement by hand.
In order to resolve the above disadvantages, it is considered that the scale holder is reduced in weight, for example, the scale holder is made of synthetic resin. In using the synthetic resin made scale holder, however, the scale having the movable detection element is adhered through the adhesive layer onto the overall surface of the scale holder, and shrinkage in cure of the adhesive layer causes warpage on the scale holder; warpage also occurs on the scale, whereby the gap between the stationary detection element and the movable detection element is changed, resulting in the difficulty of obtaining a precise measurement.
Even when the assembly with the constant gap between the stationary detection element and the movable detection element is achieved, an adhesive on the adhesive layer is repeatedly expanded and shrunk in every experiences in temperature cycles and humidity change, whereby the surface state of the movable detection element adhered is changed by the residually internal stress, resulting in precise deterioration of the products.
It is an object of the present invention to provide a measuring instrument in which the conventional disadvantages as described above are resolved, and that reduction in weight is achieved, and the disadvantages with the reduction in weight are resolved; in other words, to provide a measuring instrument in which a constant gap between a stationary detection element and a movable detection element is ensured while a processing dimension error of each component is absorbed, and which is seldom susceptible to shrinkage of an adhesive layer.